Recent vintage switching nodes that perform Layer 2 forwarding, such as bridging, classify data packets (also referred to as frames) into VLANs in order to differentiate service. Two standards have emerged for defining VLAN classification protocols, namely IEEE Standard 802.1Q entitled “IEEE Standard for Local and Metropolitan Area Networks: Virtual Bridge Local Area Networks,” 1998, and IEEE Draft Standard 802.1V entitled “Draft Standard for Supplement to IEEE 802.1Q: IEEE Standard for Local and Metropolitan Area Networks: Virtual Bridge Local Area Networks,” 2000, the contents of which are hereby incorporated by reference. Standard 802.1Q provides two basic VLAN classification rules: (1) if an inbound packet contains a tag header having a valid VLAN ID, assign the packet to a VLAN associated with the VLAN ID; and (2) if an inbound packet does not contain a tag header having a valid VLAN ID, assign the packet to a VLAN associated with the ingress port.
Standard 802.1V adopts rule (1) and modifies rule (2) as follows: if an inbound packet does not contain a tag header having a valid VLAN ID, assign the packet to a VLAN associated with the protocol type of the inbound packet from within a protocol VLAN set associated with the ingress port.
Standards 802.1Q and 802.1V also provide VLAN tagging rules for adding a tag header including an assigned VLAN ID to a packet prior to transmitting the packet on an egress port.
The provision in Standards 802.1Q and 802.1V (hereinafter referred as “Standards”) of VLAN classification rules for inbound packets that do not contain a tag header having a valid VLAN ID recognizes the possible construction of hybrid networks in which a combination of Standards-observant and Standards-unobservant switching nodes coexist. Yet there is no indication of what rules a Standards-unobservant switching node in such a hybrid network must follow in VLAN-classifying an inbound packet. For instance, it is not clear whether a Standards-unobservant switching node, such as an ingress port, should assign an inbound packet containing a tag header having a valid VLAN ID, to a VLAN associated with the VLAN ID in the packet, a VLAN associated with the ingress port, or a VLAN associated with a protocol type of the packet. It is also not clear how a Standards-unobservant switching node should VLAN-classify an inbound packet that does not contain a tag header having a valid VLAN ID.
Moreover, the Standards do not contemplate the possible construction of hybrid switching nodes including a combination of Standards-observant and Standards-unobservant ports. Additional VLAN classification questions arise in such cases. For instance, it is not clear to what extent, if any, a Standards-unobservant egress port should respect a VLAN classification decision made at an ingress port for purposes of tagging an outbound packet.
Furthermore, it is not clear how future updates and modifications to the Standards are to be handled by the switching nodes.
There is therefore a need for a VLAN classification and tagging system for a switching node that allows a degree of flexibility in defining VLAN classification and tagging rules.